of the U.S. reserves. Platinum consumption at two tons per satellite would represent about 5% of known reserves and about 2.8% of U.S. demand. The element gallium is a somewhat special case since the mass production of solar cells on the scale proposed, if made from gallium arsenide rather than silicon, would represent an increase in demand of several orders of magnitude. With almost 29 metric tons of gallium required per 10-GW satellite, each satellite would require between 24 and 182 times the projected U.S. demand in the year 2000 without the satellite. This clearly indicates a basic change in the exploration and production of this element. While other references contain numerous comments on specific aspects of resource demands, no other comprehensive treatment is available. The specific comments relate primarily to aluminum and gallium. Aluminum appears to be a material of choice for a variety of physical and electrical properties but it potentially represents a drain on known resources. Gallium is a problem by virtue of its relatively exotic nature and the very major change in its mining and manufacturing that would be required if the SSPS program were to be undertaken. It should be noted, however, that the gallium resource situation is likely to become much clearer if solar photovoltaic power technology is undertaken on a large scale for terrestrial use. The requirement for gallium arsenide is not limited to the SSPS but applies also to any widespread applications of this photovoltaic process.
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